1. Field of the Invention
The present invention relates to a microkeratome that can be used to remove tissue from a cornea.
2. Background Information
There have been developed a number of different surgical techniques to correct hyperopic or myopic conditions of a human eye. U.S. Pat. No. 4,840,175 issued to Peyman discloses a procedure wherein a thin layer of corneal tissue is cut and removed from a cornea. A laser beam is then directed onto the exposed corneal tissue in a predetermined pattern. The laser beam ablates corneal tissue and changes the curvature of the eye.
U.S. Pat. No. Re. 35,421 issued to Ruiz et al. discloses a device for cutting the cornea to expose an underlying surface for laser ablation. Such a device is commonly referred to as a microkeratome. The Ruiz microkeratome includes a ring that is placed onto a cornea and a blade that is located within an opening of the ring. The device also contains a drive mechanism which moves the blade across the cornea in a first direction while sliding the blade across the eye in a second transverse direction. The device can create a lamella which is flipped back so that the eye can be ablated with the laser.
The Ruiz microkeratome includes a head that houses the blade. The drive mechanism of the keratome moves the head and the blade across the opening of the ring. The head and ring have a pair of dovetail tongue and groove linear bearings which insure that the blade moves in a linear manner across the cornea.
The dovetail configuration of the Ruiz microkeratome requires that the head be loaded from the side of the ring. The surgeon must align the dovetail features before sliding the head onto the ring. Aligning the dovetail features can be difficult and awkward. It would be desirable to provide a microkeratome that can be more readily assembled than keratomes of the prior art.
The blade is typically assembled into a blade holder that is captured by the head of the microkeratome. The surgeon assembles the blade into the blade holder and then loads the blade holder into an opening in the head. To avoid contamination the surgeon typically holds the blade with a magnet.
It is important to accurately assemble the blade into the blade holder and load the blade holder into the head. A misalignment of the blade may result in an inaccurate cut of the cornea. It would therefore be desirable to provide a microkeratome and a tool that insure an accurate loading of the blade.
Microkeratomes that are presently used in the field typically have a stop feature that limits the movement of the blade across the cornea. The stop feature may include a pin that extends from the head and engages a stop surface of the ring. It has been found that a portion of the patient""s eyelid may fall in between the pin and the stop surface. The eyelid may prematurely stop the head and create an inaccurate cut of the cornea. It would be desirable to provide a stop feature that was not susceptible to interference from an object such as an eyelid.
Most conventional microkeratome drive mechanisms contain a plurality of spur gears that are coupled to a single drive motor. The gears rotate to move the blade and head across the ring to cut the cornea. Spur gears are susceptible to wear and crowning. Additionally, the vibration of the motor may transfer to the blade through the gears and affect the cutting action of the blade. It would be desirable to provide a microkeratome that was less susceptible to gear wear and crowning, and absorbed at least some of the vibration energy generated by the motor.
The vacuum ring typically has one or more openings that are in fluid communication with a source of vacuum. The vacuum holds the ring in place while the blade cuts the cornea. It has been found that the opening(s) may become occluded and prevent an adequate vacuum pressure to hold the ring in place during the procedure. Any movement of the ring during the cutting process may result in an improper cut of the cornea. Unfortunately, the surgeon has no means to determine whether there is an inadequate vacuum pressure at the ring/cornea interface. It would be desirable to provide a microkeratome that reduced the likelihood of an occlusion at the ring openings and provided an indication to the surgeon when there is inadequate vacuum pressure at the ring/cornea interface.
One embodiment of the present invention is a medical device that can be used to cut a cornea. The device may include a blade that is coupled to a head by a blade holder. The device may also have a retention spring that exerts a force on the blade and blade holder. The head and blade can be moved across a ring by a drive assembly that contains a lead screw. The ring may contain one or more openings which have a length that is greater than a width. The openings may be coupled to a vacuum source by a tube. The vacuum pressure of the tube can be displayed by a console. The console may also have switches that allow different operating parameters to be entered through a single knob.